Apache Module mod_mem_cache
Summary
This module is experimental. Documentation is still under
development...
This module requires the service of mod_cache. It acts as a support module for mod_cache and provides a memory based storage manager.
mod_mem_cache can be configured to operate in two
modes: caching open file descriptors or caching objects in heap storage.
mod_mem_cache is most useful when used to cache locally
generated content or to cache backend server content for mod_proxy configured for ProxyPass (aka reverse proxy).
Content is stored in and retrieved from the cache using URI based
keys. Content with access protection is not cached.
The MCacheMaxObjectCount directive sets the
maximum number of objects to be cached. The value is used to create the
open hash table. If a new object needs to be inserted in the cache and
the maximum number of objects has been reached, an object will be
removed to allow the new object to be cached. The object to be removed
is selected using the algorithm specified by MCacheRemovalAlgorithm.
Example
MCacheMaxObjectCount 13001
The MCacheMaxObjectSize directive sets the
maximum allowable size, in bytes, of a document for it to be considered
cacheable.
Example
MCacheMaxObjectSize 6400000
Note
The value of MCacheMaxObjectSize must be
greater than the value specified by the MCacheMinObjectSize directive.
| Description: | Maximum amount of a streamed response to buffer in memory
before declaring the response uncacheable |
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| Syntax: | MCacheMaxStreamingBuffer size_in_bytes |
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| Default: | MCacheMaxStreamingBuffer the smaller of 100000 or MCacheMaxObjectSize |
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| Context: | server config |
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| Status: | Experimental |
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| Module: | mod_mem_cache |
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The MCacheMaxStreamingBuffer directive
specifies the maximum number of bytes of a streamed response to
buffer before deciding that the response is too big to cache.
A streamed response is one in which the entire content is not
immediately available and in which the Content-Length
may not be known. Sources of streaming responses include proxied
responses and the output of CGI scripts. By default, a streamed
response will not be cached unless it has a
Content-Length header. The reason for this is to
avoid using a large amount of memory to buffer a partial response
that might end up being too large to fit in the cache.
The MCacheMaxStreamingBuffer directive allows
buffering of streamed responses that don't contain a
Content-Length up to the specified maximum amount of
space. If the maximum buffer space is reached, the buffered
content is discarded and the attempt to cache is abandoned.
Note:
Using a nonzero value for MCacheMaxStreamingBuffer
will not delay the transmission of the response to the client.
As soon as mod_mem_cache copies a block of streamed
content into a buffer, it sends the block on to the next output
filter for delivery to the client.
# Enable caching of streamed responses up to 64KB:
MCacheMaxStreamingBuffer 65536
The MCacheMinObjectSize directive sets the
minimum size in bytes of a document for it to be considered
cacheable.
Example
MCacheMinObjectSize 10000
The MCacheRemovalAlgorithm directive specifies
the algorithm used to select documents for removal from the cache.
Two choices are available:
LRU (Least Recently Used)LRU removes the documents that have not been accessed
for the longest time.GDSF (GreadyDual-Size)GDSF assigns a priority to cached documents based
on the cost of a cache miss and the size of the document. Documents
with the lowest priority are removed first.
Example
MCacheRemovalAlgorithm GDSF
MCacheRemovalAlgorithm LRU
The MCacheSize directive sets the maximum
amount of memory to be used by the cache, in KBytes (1024-byte units).
If a new object needs to be inserted in the cache and the size of the
object is greater than the remaining memory, objects will be removed
until the new object can be cached. The object to be removed is
selected using the algorithm specified by MCacheRemovalAlgorithm.
Example
MCacheSize 700000
Note
The MCacheSize value must be greater than
the value specified by the MCacheMaxObjectSize directive.
